626
FXUS66 KSEW 090951
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
251 AM PDT WED SEP 9 2026
SYNOPSIS
AN UPPER RIDGE OFFSHORE WILL BRING DRY, WARMER CONDITIONS ON
WEDNESDAY. TROUGHING DEVELOPS OVER THE PACIFIC NORTHWEST
THURSDAY WITH AN UPPER LOW BRINGING COOLER CONDITIONS AND
PRECIPITATION POTENTIAL INTO THE WEEKEND. MORE BENIGN WEATHER
APPEARS FAVORABLE INTO THE BEGINNING OF NEXT WEEK.
SHORT TERM /TODAY THROUGH FRIDAY/
TRANSIENT UPPER-RIDGING TODAY IN CONCERT WITH A SURFACE THERMAL
TROUGH JUST OFF THE PNW COAST. AS A RESULT, DRY CONDITIONS ARE
FAVORED AS LIGHT OFFSHORE FLOW AND SUBSIDENCE RISE TEMPS INTO
THE UPPER 70S TO LOWER 80S ACROSS THE INTERIOR - SLIGHTLY ABOVE
AVERAGE. COASTAL AREAS ARE TO STAY PUT IN THE MID TO UPPER 60S.
AFOREMENTIONED RIDGING AND SURFACE THERMAL TROUGH WILL PUSH
EASTWARD ON THURSDAY AS THE PATTERN PROGRESSES. UPPER-TROUGHING
WILL DEVELOP AS LOW-LEVEL FLOW SWITCHES ONSHORE, USHERING IN
MARINE STRATUS AND COOLER TEMPERATURES. TROUGHING FURTHER
DEVELOPS OVER THE PACIFIC NORTHWEST ON FRIDAY WITH A CONTINUED
COOLING TREND. ENSEMBLES ARE IN GENERAL AGREEMENT THAT AN UPPER
LOW MOVES SOUTHWARDS OFFSHORE FRIDAY WITH AN INCREASE OF AREAS
POPS. HIGHS FORECAST IN THE 60S AND 70S ON THURSDAY BEFORE
SETTLING MAINLY IN THE 60S ON FRIDAY. OVERNIGHT LOWS IN THE 40S
AND 50S THROUGHOUT THE SHORT TERM.
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
THE UPPER-LOW WILL MOVE INLAND OVER WA/OR DURING THE WEEKEND. RAIN
POTENTIAL INCREASES AS THE UPPER LOW MOVES INLAND, PARTICULARLY
SATURDAY INTO SATURDAY NIGHT. THERE IS ALSO A 10 TO 15 PERCENT
PROBABILITY FOR THUNDERSTORMS SATURDAY AFTERNOON. SOME
UNCERTAINTY IN THE ENSEMBLES AS TO HOW QUICKLY THE TROUGHING
MOVES EASTWARDS SUNDAY INTO MONDAY. HOWEVER, LINGERING
PRECIPITATION IS LIKELY AT LEAST OVER THE CASCADES ON SUNDAY
BEFORE A SLOW WARMING TREND BEGINS EARLY NEXT WEEK WITH RIDGING
OFFSHORE.
AVIATION
VFR CONDITIONS WILL CONTINUE ACROSS WESTERN WASHINGTON THROUGH THE
MORNING HOURS WITH PASSING HIGH CLOUDS AND LIGHT WINDS. MARINE
STRATUS AND FOG ARE EXPECTED TO DEVELOP ALONG THE PACIFIC COAST THIS
MORNING, BUT ARE NOT FAVORED TO DEVELOP OVER MOST INLAND TERMINALS.
THE EXCEPTION IS FOR KOLM/KPWT, WHERE PATCHY FOG MAY DEVELOP OVER
THESE TERMINALS IN THE EARLY MORNING. ALL INLAND TERMINALS ARE
EXPECTED TO RETURN TO VFR CONDITIONS BY 19Z, WITH HIGH CLOUDS
BEGINNING TO BUILD IN FROM THE NORTH. NORTHERLY WINDS WILL GENERALLY
REMAIN LIGHT THROUGH THE PERIOD AT 10 KT OR LESS.
KSEA...VFR CONDITIONS THROUGH THE TAF PERIOD. NORTHERLY WINDS
BETWEEN 3-6 KT OVERNIGHT, INCREASING SLIGHTLY TOMORROW AFTERNOON AT
AROUND 5 TO 9 KT WITH INCREASING HIGH CLOUDS LATER IN THE DAY.
15
MARINE
HIGH PRESSURE WILL CONTINUE TO BUILD OVER THE COASTAL WATERS THROUGH
EARLY THURSDAY, WITH A WEAK FRONTAL SYSTEM TO THE NORTH BRINGING
INCREASED NORTHWEST WINDS OVER THE COASTAL WATERS AND A PUSH THROUGH
THE STRAIT OF JUAN DE FUCA. WESTERLY WINDS WILL REACH SMALL CRAFT
STRENGTH THROUGH THE STRAIT LATE WEDNESDAY EVENING THROUGH THURSDAY
MORNING, AND A SMALL CRAFT ADVISORY HAS BEEN ISSUED. WINDS WILL
GRADUALLY EASE INTO THURSDAY NIGHT ACROSS ALL AREA WATERS. ANOTHER
WEATHER SYSTEM IS ON TRACK TO CROSS THE WATERS LATE FRIDAY IN TO
SATURDAY, BUT NO SIGNIFICANT IMPACTS OR HEADLINES ARE ANTICIPATED AT
THIS TIME.
SEAS AROUND 4 TO 5 FEET WILL CONTINUE TO GRADUALLY BUILD INTO
THURSDAY, REACHING 8 TO 11 FEET ACROSS THE OUTER WATERS. A SMALL
CRAFT ADVISORY HAS BEEN ISSUED TO ACCOUNT FOR THESE WAVES, WHICH
WILL BE STEEP WITH A PERIOD OF 8 TO 10 SECONDS. SEAS WILL EASE TO
AROUND 4 TO 6 FEET BY FRIDAY, WITH RELATIVELY CALM SEAS INTO THE
WEEKEND.
FIRE WEATHER
A DRYING AND WARMING TREND WILL PEAK TODAY, WITH LIGHT EASTERLY FLOW
THROUGH THE CASCADE GAPS CAUSING MODERATE OVERNIGHT HUMIDITY
RECOVERIES ALONG THE WESTERN CREST OF THE CASCADES. DAYTIME RELATIVE
HUMIDITIES ALONG THE RIDGES OF THE CASCADES AND OLYMPICS WILL BOTTOM
OUT IN THE LOW TO MID 20S, CAUSING BRIEF ELEVATED FIRE WEATHER
CONCERNS FOR THESE AREAS. HOWEVER, THIS WILL BE SHORT LIVED, WITH
ONSHORE FLOW RETURNING ON THURSDAY AS A WEAK AND MOSTLY DRY FRONTAL
SYSTEM CROSSES TO THE NORTH. COOLER AND MORE MOIST CONDITIONS WILL
RETURN OVER THE WEEKEND, WITH PERIODIC CHANCES FOR LIGHT
PRECIPITATION.
15
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 AM PDT
THURSDAY FOR CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-
EAST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 5 AM THURSDAY TO 5 AM PDT FRIDAY FOR
COASTAL WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO
60 NM-COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE
10 TO 60 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE
SHOALWATER 10 TO 60 NM.
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